100 Transactions of the South African Pliilosophical Society. 



leaving the country on the southern side of the vent uncovered, but 

 it is easily seen how this state of affairs has arisen. Take, for 

 instance, the volcanic range of hills east of Honolulu in the Hawaiian 

 Islands. This range runs N.W., S.E. The eastern side bears the 

 full brunt of the trade winds, and it is on this side that nearly all 

 the rainfall of the island occurs ; the high mountains wring from the 

 trade wind all its moisture, and consequently as it blows over the 

 western part of the island it assumes the character of a dry wind ; 

 the eastern side is therefore intensely eroded, presenting a gigantic 

 cliff which, except at one point in the whole range, is hardly 

 accessible to human foot, while the western side is gently inclined 

 and has the appearance more of a sloping plateau than part of a 

 mountain range. The same action has gone on in the Drakensberg. 

 When the volcanic peaks towered up in a long line running in a 

 north-easterly direction they caught the full blast of the rainy south- 

 easters, w^hich precipitated their moisture on the windward side ; on 

 the leeward side the rainfall was slight, consequently the windward 

 slopes of the mountain were eroded at a great rate, while the lee- 

 ward was gently carved out by the denuding action of running 

 water, and formed an incised plateau, a character which Basutoland 

 still expresses. The windward side, therefore, became steeper and 

 steeper ; great falls of rock occurred, which were carried away to sea 

 by the impetuous mountain torrents, and presently the very centres 

 of the volcanoes were exposed, and eventually the progress of erosion 

 continued further till only the northern slopes of the old volcanic 

 pile contributed to form the mountain chain, and the vents, no 

 longer situated in the loftiest portion of the range, got worn down 

 and down till most of them are now found at the lowest levels at the 

 foot of the mountains. Some, however, strengthened by a weather- 

 resisting backbone of solidified lava, held out longer than the rest, 

 and now occupy outstanding positions on the flanks of the moun- 

 tains, and these form the most interesting ones of the series, as it is 

 in these that one can trace the lava-flows and other surface features. 

 I will not go into details of all the varieties of vents with the 

 particular rocks that each contains ; that information will be 

 embodied in the usual Annual Eeport of the Geological Commission, 

 but I will take one or two cases from which the general nature of 

 these volcanoes can be understood. One of the best of the agglo- 

 merate pipes occurs on a farm, " Deer Park," belonging to a Dutch- 

 man named Bekker, who had for a long time speculated on the 

 nature of this peculiar jumble of all sorts of rocks ; it is just in front 

 of his house, and forms a very conspicuous object along the road. 

 The pipe is about a quarter of a mile in transverse section, and is 



